Electrical control system



A. PFISTER Filed 001;. 14, 1932 R M WW m mw /m m Em i b Q A Q 0/ Y B ELECTRICAL CONTROL SYSTEM Jan 7 1936,

Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE to Radio Corporation of Delaware of America, a corporation Application October 14, 1932, Serial No. 637,715

1 Claim.

This invention relates to the synchronization, with a single controlling frequency source, of one or more local oscillators, such as are used for controlling the frequency of a broadcast transmitting station.

The principal object of my present invention is to provide an improved phase or frequency synchronizing system for the control of a local oscillator in accordance with currents supplied from a substantially constant frequency controlling source or tone. Briefly, this object is fulfilled by combining, 90 degrees out of phase, a portion of the locally generated energy with a portion of the controlling energy to obtain a resultant alternating current. This current is rectified and is used to electromechanically vary a tuning element included in the local oscillator to shift its phase and/or frequency in such a way that the 90 degree phase relationship between the combined alternating currents will be maintained.

In the customary synchronization system, as the control tone is usually fed over lengthy land lines adjacent to other communication circuits it is subject to occasional momentary phase shift, level change and even failure. An already existing method of synchronization operating on the principle of locking the control and local frequencies together, whereby the controlling frequency exercises government, is to a large degree, subject to the above mentioned hazards as is well known to those skilled in the art. To prevent the undesired effects of such occurrences is a further object of my present invention and to do so I provide three means, the first of which is represented by a circuit responsive to failure in the supplied control tone which will render inoperative the frequency varying arrangement of my present invention and allow the local oscillator to continue undisturbed at approximately the correct operating frequency. The second means act whenever phase disturbances enter the control tone by limiting, by means of a mechanism having high inertia the rate at which such phase changes can occur. The third means provide for supply of a constant level of control tone regardless of level fluctuations at the source or conveying medium. Such operation clearly is far more desirable than having the locally generated waves and hence the transmitted radio frequency waves in the case of a synchronized broadcasting station, shift through a frequency range which might interfere with other stations of the syn chronized chain.

My present invention is described more fully with the aid of the accompanying drawing where- 1n,

Figure 1 is a wiring diagram of a broadcasting station whose phase and/or frequency is syn chronized, in accordance with the teachings of my present invention, with the phase and/or frequency of a supplied control tone or alternating current; and,

Figures 2, 3 and 4 inclusive are explanatory of the phase controlling arrangement utilized in Figure 1.

Turning to Figure 1, electron discharge device or vacuum tube oscillator tube 2 is regeneratively associated through inductance coils 4, 6 with an electromechanical frequency controlling vibrator 8 in the form of a tuning fork. The oscillator 2 is provided with an output circuit [0 having a choke coil 12. Shunted across coil 4 is a tuning and/or phase adjusting condenser l4 which in turn is shunted by phase and/or frequency controlling condenser l6.

Output energy from the local oscillator 2 is fed through blocking condenser l8 to a further buffer and reaction preventing amplifier 20 in whose output circuit there is provided a transformer 22 25 feeding the locally generated oscillatory energy to succeeding amplifiers 24 and frequency multipliers 26. Frequency multipliers 26 build up the locally generated energy in frequency to a sufficiently high radio frequency value. The fre- 30 quency multiplier output or radio frequency energy is modulated in a suitable modulator 28, amplified in power amplifier 30 and radiated over any suitable antenna 32.

To maintain synchronism between the waves radiated over antenna 32 and, if desired, other broadcasting stations, the phase or fundamental frequency generator 2 is tuned to keep in step with energy of a control frequency supplied from a source 34 over land lines 36. A portion of the control tone or alternating current received from source 34 over land line 36, for frequency tuning purposes is amplified by an amplifier 38 which, in its preferred form is of the automatic volume control type so as to supply energy of constant level to transformer 40 and electron discharge device amplifier 50. Somewhat similarly a portion of the locally generated base frequency or tone is fed through transformer 22 and secondary 42 through conductors 44 and transformer 46 to electron discharge device amplifier 4B.

Condenser 14 of local oscillator 2 is adjusted so that, at a time when local oscillator 2 and the control source 34 are of like frequency, the

- means (not shown) currents or potentials fed to the tubes or amplifiers 48, 50 will be in quadrature or 90 degrees out of phase, and of substantially like amplitude through the adjustment of the volume control resistors or potentiometers 52, 54. The application of equal intensity voltages to the amplifiers 48, 50 will be indicated by like readings in milliammeters 56, 58. The method of accurately obtaining the 90 degree phase relationship of voltages applied to the amplifier 48, 50 will be described shortly. I

As shown, the outputs of the amplifier tubes 48, 50' are combined in the secondary of transformer 60 and rectified by rectifier 62. The direct current output of rectifier 62 is fed through choke coil 64 to galvanometer or floating coils 66, 68 pivotally mounted upon a supporting bar 70 and fulcrum I2. To the bar 10 there is attached a spiral spring I4 whose tension may be adjusted by any suitable adjusting screw or The coils 66, 68 are connected together serially so that with varying current flows supplied by rectifier 52, they will rotate about fulcrum- 12 due to magnetic interaction with permanent magnet IS.

The floating bar I and coils 66, 68 are also provided with a pointer I8 and scale 30. The scale is calibrated so as to cover the cosine function of angular phase displacement of currents fromthe local oscillator 2 and the control source 34. That is, the scale is arranged to read zero at its center, and extreme movements of indicator I8 to either side of the center indicate respectively, plus 1 and minus 1.

Consequently, by discreet choice of constants for the circuits as so far described, equal values of voltages impressed upon the control electrodes of tubes 50, 48 will cause a zero reading upon scale so when these alternating potentials impressed upon control electrodes of amplifiers 48,

i 50 are exactly 90 degrees out of phase.

In other words, referring to Figure 2, with the resultant input voltage E50 applied to tube 50 and with the resultant input voltage E48 applied to vacuum tube 48, the resultant alternating voltage appearing in the secondary of transformer 60 will be indicated by the vector Er.

With the application of such a resultant voltage to rectifier tube 62, the contacts 90, 92 are caused to remain open through adjustment of tension on spring 14.

However, with very small frequency drifts, which as a matter of practice amount to less than a single cycle and hence are only phase shifts, of the locally generated voltage of source 2 with respect to the voltage derived from source 33, the resultant voltage applied to the rectifier 62 varies as shown in Figures 3 and 4. Consequently, due to increased and decreased current flows through the coils 66, 08 bar I0 will swing either clockwise or counter-clockwise dependent upon the magnitude of the current flowing in the coils 66, 69. With variations in current flow away from the mean desired operating value of current in the output circuit of rectifier 62, either contact 90 or contact 92 will be closed dependent, of course, upon the magnitude of current flowing through the coils 66, 6B and the relative polarity of the permanent magnet I6 with respect to the current flowing in the coils.

Matters should be arranged such that upon closure of either contact 90 or 92, reversible motor 96 will be actuated in such a direction as to rotate, through gear reduction box 96, shaft 98 in the proper direction to cause variable phase adjusting condenser I6 to bring the phase of oscillations generated by generator 2 back into the desired 90 degree phase relationship with oscillations from source 34. As a preferred adjustment, full scale deflection of indicator 18 should cause a 180 rotation of condenser I6.

To prevent over-running of motor 94 it is provided with a continuously applied electrical brake (and/or the gear box 96, should be provided with some form of damping means, such as a dashpot, as a continuously applied brake).

The arrangement described may be repeated at other stations supplied with control energy through branch lines IOI, I02. For the sake of simplicity, the controlling apparatus for the statons supplied with energy from the lines IOI, I02 have not been illustrated.

To prevent haphazard and undesired hunting or drifting of the frequency or phase controlling 20 .mechanism in the event of failure of tone from the control source 34, I have provided, serially connected with the anode or plate of tube 50, a solenoid I03, cooperatively associated with an armature or switch I04. Presence of control tone will cause plate current flow, (due to the fact that the tubes 48, 50 are normally biased to. cut-off by polarizing source 100) through solenoid I03 and hence closing of switch I04 allowing actuation of two way motor 94. 7

However, in the absence of control tone switch I04 will open as shown as a result of which motor 94 and the phase or frequency adjusting condenser or reactor I6 will be rendered inoperative.

Furthermore, to prevent haphazard and un- 85 desired hunting or drifting of the frequency or phase controlling mechanism in the event of erratic phase disturbances of the control tone in its transit from source 34 to amplifier 38, I have provided mechanical time delay, such as a dash-' i0 pot, in reduction gear box 96 to slow up movement of phase adjuster IS with respect to its 'driving motor 95 to a sufficient degree to render out of phase, are fed through amplifiers 43,

to rectifier 62. Equal intensity currents are in- 50 dicated by milliammeter 55, 58 and, the 90 degree phase relationship is obtained by adjustment of condenser I l until pointer 78 of the galvanometer arrangement 66, 03, i9 is at its mid position. Drifts in relative phase in oscillations from the control source 34 and local oscillator 2 will manifest themselves in current flows in the output circuit of rectifier 62 away from the mean value of current obtained when the voltages applied to tubes 98, 50 are of like intensity and 90 degrees out of phase. Consequently, variation in current flow away from the mean value will cause closing of either contact 90 or 92 and hence rotation of motor 94 in one direction or another. The direction of rotation will be such as to adjust oscillator 2, through the medium of phase or frequency control condenser IE, to become tuned to the desired 90 degree phase or frequency synchronism with the control source 36.

In the event of failure of energy from the control source 34, solenoid I03 becomes deenergized allowing switch I04 to open thereby cutting out of circuit motor 94 and hence preventing continuance of rotation of variable reactor I6.

Having thus described my invention, what I claim is:

In an alternating current control system, a synchronizing source of oscillations and a local source of, oscillations of approximately the same frequency as said synchronizing source, a first transformer having primary and secondary windings and a second transformer having primary and secondary windings, said synchronizing source being connected to the primary winding of said first transformer and said local source to the primary winding of said second transformer, a resistance connected across each secondary winding, a connection between said resistances, a pair of electron discharge devices each having anode, cathode and grid electrodes, the grid of one device being tapped to a point on one of said resistances intermediate its ends, and the grid of the other device being similarly tapped to the other resistance, the cathodes of said devices being connected together and to a point on the connection between said resistances, a third transformer having primary and secondary windings, one end of,said last primary winding being connected to an anode of one of said devices and the other end of said primary winding being connected to the anode of said other device, a source of anode potential between said cathodes and the center of said last primary winding, a rectifier coupled to said secondary winding of said third transformer for rectifying the combined energies obtained from said two devices, means including a motor for varying the electrical constants of said local source of oscillations in either of two senses for restoring any departure of said local source from a predetermined relationship with respect to the synchronizing source, and means including a mechanical relay connected to said rectifier and responsive to a change of rectified energy therein of a value difierent from the resultant value obtained when a 90 phase relationship exists between energies of the two sources applied to said grids for driving said motor to compensate for said change, a switch comprising normally open contacts having an energizing winding connected be tween one end of the primary winding of said third transformer and the anode of that device whose grid is in circuit with said synchronizing source, said motor being connected through the contacts of said switch, means for biasing the grid of that device whose grid is in circuit with said synchronizing source substantially to out 01f, whereby said energizing winding is normally responsive to the flow of current in said last mentioned device, due to said synchronizing source for closing its contacts, whereby the influence of said motor on said local source is only effective during continued current flow from said synchronizing source.

ARTHUR PFISTER. 

